Dash Air Not Working

Why don't you just have a HVAC shop replace it if you are not sure what's going on?

Yes the system has the proper amount of R134A - low pressure switch is ok (closed). Have yet to test the high pressure switch.

Going back to the schematic - this is a Denso wiring diagram I got by getting the part number off the dash control and searching the web. The schematic is for the interior heat/cooling unit inside the cockpit. According to Tiffin AC service tech the Denso unit sends a 12V signal (the output of the "Magnetic Clutch Relay" pin 3 at top of page) to the Workhorse chassis. I believe the part shown to the right of the label "Light Switch" is a generic destination since Denso doesn't know what vehicle their unit is installed in.
Under the hood the diagram in the cover of the fuse center shows a 10A fuse labeled "Comp" and a relay labeled "Comp". This fuse and relay feed the compressor clutch.
When I depress the AC ON button on the control panel it applies 12V to one side of the coil and to the contacts. All I need is a ground to the other side of the coil - this must come from Workhorse installed sensors like the Hi and Low pressures switch's.
As a retired EE I have 48 years electrical experience and I am EPA certified in HVAC including mobile - but without a schematic for the Workhorse side I am flying blind.
Since there is protection for pressure and temperature in the Denso unit I think I can safely permanently ground the relay coil under the hood and forget figuring out what it should be..............

When you jump this relay have you had gauges connected to the service ports to determine if there is any Freon in the system ? It would appear that the low pressure switch is open. Have you jumped across this switch to see if the compressor engages?

Westend:

Thanks for the reply - Yes this is the correct schematic for my MH. There are no WH service centers nearby. Tiffin no longer takes appointments. You have to go to Red Bay where it is first come first served. You could sit in their campsite for several days before even being called.
Since 12V is present on one side of clutch relay coil (the one I can short across and get compressor to come on) all I need is a ground on the other side. The schematic shows the destination of the 12V from the interior unit to the right of "Light Switch" on right side of drawing. Don't know what that is and where it is.

OK, I was able to download the schematic referenced in the original post. It is here, for those wishing to follow along. OP, please verify that this is the correct schematic on Page 36 for your Allegro.

The schematic shows a single main ground point for the A/C functions. The ground is connected to a terminal block (Pos. 24, WB) and then connected to the other devices in the system.

Suspect also, if clutch won't engage would be the main relay as I believe power to the clutch relay is from the main relay.

Is there something problematic about taking the RV to a Workhorse service center?

Used a test relay that can short across the contacts and send 12V to compressor clutch and everything works OK.

Wouldn't that indicate that the onboard HVAC relay had failed? Do you have other relays on a distribution board? Are those relays working?

Without the schematics and pictures shared, you'll probably get either little response or generic information like mine.